The mechanism of low-temperature deformation in a fracture process of Ll2 Ni3Al is studied by molecular dynamic simulations. Owing to the unstable stacking energy, the [011] superdislocation is dissociated into partial dislocations separated by a stacking fault. The simulation results show that when the crack speed is larger than a critical speed, the Shockley partial dislocations will break forth from both the crack tip and the vicinity of the crack tip; subsequently the super intrinsic stacking faults are formed in adjacent {111} planes, meanwhile the super extrinsic stacking faults and twinning also occur. Our simulation results suggest that at low temperatures the ductile fracture in Ll2 Ni3Al is accompanied by twinning, which is produced by super-intrinsic stacking faults formed in adjacent {111} planes.
Using the first-principles self-consistent discrete variational method based on density functional theory, we investigated the effect of light impurities C and N on the electronic structure of kink on the [100](010) edge dislocation (ED) in bcc iron. Our energetic calculations show that the light impurities have a strong segregation tendency to enter the kink. The results of the charge distribution and the local den-sity of states indicate that the strong bonds between the impurity atoms and the neighboring Fe atoms are formed due to the hybridizations of impurity atoms 2p states and Fe 3d4s4p states. The introduction of light impurities can stabilize the kink system, and impedes the sideward motion of the kink in the [100](010) ED. This is, the light impurities induce a strong pinning effect on the [100](010) ED and may result in the solid solute hardening.
采用质点网格法(particle in cell),利用MAGIC软件模拟了场致发射的物理过程.对两种典型的场致发射模型(Spindt阴极发射体和金刚石薄膜发射体)分别进行了模拟.对Spindt阴极发射,研究了发射特性与尖端尺寸,尖端与栅极面的相对高度的关系.对金刚石薄膜发射,比较了三极管和四极管的发射特性,以及薄膜面积对发射特性的影响,得出金刚石薄膜发射体优于Spindt发射体的特性.
In this article the hard-sphere Discrete Particle Model （DPM） is used to study the mixing behavior of particles in the 2-D fluidized bed. Different flow patterns in the bed for two kinds of inlet configurations, namely free bubbling and jet bubbling mode, are captured by the numerical model, under specific superficial gas velocities. To examine the degree of particle mixing, the Fan index is applied. The numerical results show that the rate of particle mixing is larger in the jet bubbling than that in the free bubbling mode. The gross circulations of particles in the jet bubbling bed give a higher degree of mixing because of the involvement of a greater number of particles.
Using the molecular dynamics method,we have constructed two kink models corresponding to the 〈100〉{010} and 〈100〉{011} edge dislocations (EDs) in body centred cubic (bcc) Fe. It is found that the geometric structure of a kink depends on the type of edge dislocation and the structural energies of the atoms sites in the dislocation core region. The formation energies,migration energies and widths of the kinks in different types of EDs are calculated. The results show that formation and migration of the kink in the 〈100〉{010} edge dislocation are difficult. The 〈100〉{011} edge dislocation moves primarily through kink nucleation,rather than kink migration.
CHEN LiQun1,2,WANG ChongYu2,3,4 & YU Tao2 1 College of Sciences,Central South University of Forestry & Technology,Changsha 410004,China
